1. Technical Field
The present invention relates to a virtual image display device such as a head-mounted display used while worn on the head.
2. Related Art
In recent years, as a virtual image display device such as a head-mounted display for making formation and observation of a virtual image possible, there have been proposed various devices, which are a type of guiding the image light from a display element to the pupils of the observer using a light guide plate.
In such a virtual display device, in order for overlapping the image light and the external light, there has been proposed a see-through optical system (see, e.g., JP-A-2010-224473 (Document 1)).
However, in the device described in Document 1, since the see-through property is realized by a pupil division method using a light guide optical system with an emission opening smaller in size than the pupil, it is difficult to increase the display size of a virtual image. Further, since the light guide optical system smaller in size than the pupil is used, it is difficult to increase the effective pupil diameter (which is the lighting diameter for enabling acquisition of a virtual image, and is also referred to as an eye ring diameter) in order to correspond to individual human pupil distance. Further, since the emission opening and the housing of the light guide optical system are arranged in the physical vicinity of the pupil, a blind area is caused, and it cannot be called a perfect see-through state.
It should be noted that as an optical system for a head-mounted display, there has existed a system provided with a light guide member capable of making a plurality of optical modes different in light guide angle proceed (see JP-T-2008-535001 (Document 2). In such an optical system as described above, it is also possible to adopt a half mirror as a third optical surface on the exit side, and flatten the entire surface by attaching a prism-like member to the light guide member so as to bury the half mirror inside to thereby modify the system into a see-through light guide device enabling the observation of the external light through the half mirror.
However, there is a possibility that a strong force is applied to the part where the light guide member and the prism-like member are bonded to each other, and if the bonding strength between the members is not sufficient, exfoliation is caused in the bonded part, and there is a possibility of damaging the light guide device.